/*
* Copyright 2011-2018 Blender Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

CCL_NAMESPACE_BEGIN

ccl_device_noinline float svm_ao(KernelGlobals *kg,
                                 ShaderData *sd,
                                 float3 N,
                                 ccl_addr_space PathState *state,
                                 float max_dist,
                                 int num_samples,
                                 int flags)
{
	if(flags & NODE_AO_GLOBAL_RADIUS) {
		max_dist = kernel_data.background.ao_distance;
	}

	/* Early out if no sampling needed. */
	if(max_dist <= 0.0f || num_samples < 1 || sd->object == OBJECT_NONE) {
		return 1.0f;
	}

	/* Can't raytrace from shaders like displacement, before BVH exists. */
	if (kernel_data.bvh.bvh_layout == BVH_LAYOUT_NONE) {
		return 1.0f;
	}

	if(flags & NODE_AO_INSIDE) {
		N = -N;
	}

	float3 T, B;
	make_orthonormals(N, &T, &B);

	int unoccluded = 0;
	for(int sample = 0; sample < num_samples; sample++) {
		float disk_u, disk_v;
		path_branched_rng_2D(kg, state->rng_hash, state, sample, num_samples,
		                     PRNG_BEVEL_U, &disk_u, &disk_v);

		float2 d = concentric_sample_disk(disk_u, disk_v);
		float3 D = make_float3(d.x, d.y, safe_sqrtf(1.0f - dot(d, d)));

		/* Create ray. */
		Ray ray;
		ray.P = ray_offset(sd->P, N);
		ray.D = D.x*T + D.y*B + D.z*N;
		ray.t = max_dist;
		ray.time = sd->time;

		if(flags & NODE_AO_ONLY_LOCAL) {
			if(!scene_intersect_local(kg,
			                          ray,
			                          NULL,
			                          sd->object,
			                          NULL,
			                          0)) {
				unoccluded++;
			}
		}
		else {
			Intersection isect;
			if(!scene_intersect(kg,
			                    ray,
			                    PATH_RAY_SHADOW_OPAQUE,
			                    &isect,
			                    NULL,
			                    0.0f, 0.0f)) {
				unoccluded++;
			}
		}
	}

	return ((float) unoccluded) / num_samples;
}

ccl_device void svm_node_ao(KernelGlobals *kg,
                            ShaderData *sd,
                            ccl_addr_space PathState *state,
                            float *stack,
                            uint4 node)
{
	uint flags, dist_offset, normal_offset, out_ao_offset;
	decode_node_uchar4(node.y, &flags, &dist_offset, &normal_offset, &out_ao_offset);

	uint color_offset, out_color_offset, samples;
	decode_node_uchar4(node.z, &color_offset, &out_color_offset, &samples, NULL);

	float dist = stack_load_float_default(stack, dist_offset, node.w);
	float3 normal = stack_valid(normal_offset)? stack_load_float3(stack, normal_offset): sd->N;
	float ao = svm_ao(kg, sd, normal, state, dist, samples, flags);

	if(stack_valid(out_ao_offset)) {
		stack_store_float(stack, out_ao_offset, ao);
	}

	if(stack_valid(out_color_offset)) {
		float3 color = stack_load_float3(stack, color_offset);
		stack_store_float3(stack, out_color_offset, ao * color);
	}
}

CCL_NAMESPACE_END
